Two areas of research are currently being pursued in the Auditory Research Lab: 1) the use of otoacoustic emissions (OAEs) to probe auditory efferent function, and 2) the measurement and quantification of certain electro-acoustic characteristics of hearing aids.
Otoacoustic Emissions. Efferent neural systems can adjust the mechanics of the cochlea and modify the way sound is processed by the auditory system. The functional effects of these modifications are not fully understood, but they are believed to influence hearing in noisy situations and may also provide some protection from the effects of exposure to loud noise. OAEs are very soft sounds that arise as a by-product of normal cochlear function and can be recorded using tiny loudspeakers and microphones placed in the ear canal. Modulation of cochlear mechanics by auditory efferent activity causes changes in OAE amplitude and phase. This provides a non-invasive, indirect measure of efferent effects on auditory function.
Hearing Aids. The continual improvement of digital technology has made possible the implementation of many innovative signal processing algorithms. Many of these are adaptive, and some hearing aids alter their processing based on an ongoing analysis of the temporal and spectral properties of incoming sound. With these new adaptive processing schemes, some of the older methods of quantifying hearing aid performance may no longer be appropriate. Current efforts are aimed at specifying methods that can accurately describe hearing aid performance in situ. Such methods may have useful clinical applications.
The ARL is equipped for acoustic measurements and analysis. The laboratory space includes a 9' X 8' double-walled sound booth. The lab also has access to the department's anechoic chamber. Measurement equipment includes a Larson Davis 824 sound level meter, G.R.A.S. IEC 711 ear simulator, KEMAR acoustics research mannequin, and Etymotic Research ER-10B+ and ER-10C otoacoustic emissions probes. Data acquisition is typically made using a Lynx L22 sound card , PC with Windows XP, and custom software written in MATLAB. Various TDT System 3 components are also used, including HB7 headphone buffers, MA3 microphone amplifier, SM5 signal mixer, and PA5 programmable attenuators that can be controlled from MATLAB using ActiveX. Signal processing and data analysis are done with MATLAB. For audiometric testing, the ARL has a Madsen Equinox diagnostic audiometer and a GN Otometrics Otoflex 100 impedance bridge. The lab also has access to an AudioScan Verifit probe microphone system, NOAH software, and a HiPRO interface for programming hearing aids.
Auditory Research Laboratory
Dr. Shawn S. Goodman, Director
341 Wendell Johnson Speech and Hearing Center
The University of Iowa
Iowa City IA 52242
(319) 335-8761
e-mail
